High-frequency wave meter



March 13, 1951 J. P. HAGEN ETAL 2,544,674

HIGH-FREQUENCY WAVE METER Filed Aug. 27, 1943 lEr l.

wuc'no/td JOHN P HAGEN FRANK G SELY Patented Mar. 13, 1951 HIGH-FREQUENCY WAVE METER John P. Hagen, Arlington, Va., and VFrank C. Isely, Washington, D. C.

Application August 27, 1943, Serial No. 500,230 7 claims. o1.25o39) (Granted under the act of March 3, 1883, as

This invention relates to a Vmeans for measuring wave length of ultra high-frequencies and more particularly to a high Q coax al conductor wavemeter having means for automatically controlling the effects of varying conditions yof temperature and humidity on Wave measurements.

It is now well known to those skilled in the art that the vel-ocity of propagaton of electromagnetic waves is a function of the dielectricy constant of the medium through which the wave travels. Therefore wavemeters th t utilize the principle of reflection, such as the parallel Wire system which usually employ a microammeter to measure the distance between voltage maximas and consequently Wave length, are subject to the effects of changing conditions of humidity which is a change in the dielectric constant of the ambient medium and consequently a change in the velocity of propagation. This change in propagation velocity is obviously one of the greatst sources of error since the Wave length for a given frequency will undergo a corresponding change. Moreover wavemeters of this type are subject to stray electromagnetic fields and hand capacities which also operate to reduce the accuracy of the wave length measurement.

Thus it is contemplated by the present invention to provide a non-radiating wavemeter having means for controlling the effects that varying conditions ofv humidity have on wave`measurements. It is also contemplated by the present invention to provide a coaxial conductor wavemeter having means for maintaining the length vof the inner conductor and consequently the resonant frequency constant over a wide range of temperature variations.

It is therefore an object of this invention to provide a high Q wide frequency range wavemeter.

It is another object of this invention to provide a cavity wavemeter having incorporated therewith a means for controlling the effects of changing conditions of humidity.

It is another object of this invention to provide a means for maintaining the inner conductor and amended April 30, 1928; 370 O. G. 757) Referring to the ligure wherein there is shown a preferred embodiment of the present invention comprising a coaxial conductor wavemeter having cylinders I and 2 of different diameters, concentrically disposedone within the other. The outer cylinder I is shorted at one end by the metallic disc member 3 and at the opposite end by the metallic disc member 4. The inner cylinder 2 is concentrically supported at one end within the outer cylinder I in a manner similar to a cantilever beam support. There is also associated with the inner cylinder 2 a telescopic member 5 shorted at one end by disc 6, which is in effect a continuation of the inner cylinder 2. Thus, hereinafter we prefer -to call the inner cylinder 2, and the telescopic member 5, the inner member When referred to jointly. In order to provide constant electrical contact between the inner cylinder 2 and the telescopic member 5 a cylindrical therefore the resonant frequency of a coaxial conductor wavemeter constant over a wide range vof temperature changes.

Other objects and features of the present invention will become apparent 1111011 a Careful C011- siderati-on of the following detailed description when taken together with the accomranyn'g drawing, the single iigure of which is designed for the purpose of illustration only, and not as a definition of the limits of the invention, reference for the latter being had to the appended claims,

flexible flange member 'I is permanently secured at one end to the inner cylinder 2 and slotted at the other 'end to provide a plurality of fingers which are maintained in sliding electrical contact With the telescopic member 5. There is also con- -centrically disposed within the inner cylinder 2 a threaded Invar bar -8 which is mechanically coupled at one end to a graduated dial 9 and at the opposite end to a nut I0 which is permanently secured to the telescopic member 5. The nut I0 is provided with a pair Yof diametrically opposite keys IVI and II which are adapted to t a pair of diametrically opposite longitudinal key ways I2 and I2 cut in the inner surface of the inner cylinder Y2 to prevent rotation of the telescopic member 5 with rotation vof the Invar bar 8. The primary reason for preventing rotation of the telescopic member 5 is to prevent uneven and excess wear of the flange 1 which would, in time, pro-J duce a bad electrical contact between the ange 1 and the telescopic member 5. There is also associated with the Invar bar 8 a pair of ball bearings -I3 and I3' which operate to prevent back lash of the Invar bar 8 upon rotation of the dial 9. A bevel gear arrangement I4 is also coupled to the Invar bar 8 and to a mechanical counter I5 to maintain anA accurate count of the number of revolutions the Invar rod has been turned by the dial 9. There is also associated with the graduated dial 9, a Vernier I6 which provides an accurate reading of the dial setting. This dial, like the mechanical counter I5, may be calibrated in frequency or wave length since rotation of the Invar bar regulates the position of the telescopic member 5 With respect to the free end of the inner cylinder and therefore the physical over-all length of the inner member, which in turn varies the resonant frequency of the wavemeter. As previously mentioned the velocity of electromagnetic wave propagation is a function of the humidity of the air through which the Wave travels, and therefore should be maintained constant for the most accurate results during a frequency or Wave length measurement. Thus there is provided a means for maintaining the humidity of the air in the chamber of cylinder i at a constant value, comprising the retaining cylinder I1 designed to receive any suitable drying agent, such as for example, Dryrite calcium chloride or silica gel. A transition piece I8 joins cylinder I1 to cylinder i and exposes the contents of cylinder I'I to the air of the chamber of the cylinder I. The drying agent contained in this cylinder is preferably inserted in the form of a capsule so as to facilitate replacement thereof.

From the foregoing description it becomes obvious that the present system of maintaining the humidity constant can be used with any wavemeter that is enclosed in a suitable retaining chamber.

It is also realized by those skilled in the art that changes in ambient temperature operate to change the physical length of the inner member which produces a change in resonant frequency. Thus there is provided the Invar bar 8 which is constructed of any suitable material having a low coeiiicient of expansion and thereby remains substantially constant in length regardless of temperature variations. Consequently as cylinder 2 tends to expand or contract with variations in temperature the length of the Invar barA remains constant to allow cylinder 2 to move longitudinally along the telescopic member 5 and thereby maintain the over-all length of the inner member constant. l

The operation of the present wavemeter is as follows: an exciting means or resonating source is coupled to loop i9 which is projected into space surrounded by the outer cylinder I through grommet 20, while the output is taken from loop 2l which is also projected into the cylinder by way of grommet 22. The output is fed through a detector circuit, not shown here, which may be either a crystal or vacuum tube detector, to a microammeter 23. Dial 9 is rotated and consequently the physical length of the inner member varied until peak deflection is noted on the meter 23, which indicates resonance has been obtained. The length of the inner member at this point is generally one-quarter wave since this is the smallest fraction of a wave length capable of producing resonance. The frequency or wave length is then read or interpolated from the dial 9 and or mechanical counter I5.

The input and output loops I9 and 2 I comprise loose coupling circuits which do not impair the inherently high Q of the Wavemeter nor allow loading on the external circuit to affect the resonant frequency of the wavemeter .thereby making the present device a sensitive, reliable, compact wavemeter.

Although We have shown and described but one embodiment of the present invention we are fully aware of the many modifications possible thereof. Therefore this invention is not to be restricted except insofar as is necessitated by the prior art and the spirit of the appended claims.

The invention described herein may be manuiactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

We claim:

'1. A coaxial conductor Wavemeter, comprising a pair of cylinders of diierent diameters concentrically disposed one within the other and shorted at one end by a metallic disc, a second metallic disc closing the opposite end of the outer cylinder in a manner to form a closed air chamber, input and output coupling means projected into the space surrounded by said outer cylinder, indicating means connected to said output coupling means for measuring current in said air chamber, and hygroscopic means exposed to said air chamber but disposed outside thereof to maintain a constant velocity of propagation within said air chamber.

2. A coaxial conductor Wavemeter, comprising a pair of cylinders of different diameters concentrically disposed one within the other and shorted at one end by a metallic disc, a second metallic disc closing the opposite end of the outer cylinder in a manner to form a closed air chamber, input and output coupling means projected into the space surrounded by said outer cylinder, and hygroscopic means exposed to said air cham- 'ber but disposed outside thereof to maintain a constant velocity of propagation within said air chamber.

3. A coaxial conductor wavemeter, comprising a pair of cylinders of different diameters concentrically disposed one Within the other and shorted at one end by a metallic disc, a second -metallic disc closing the opposite end of the outer cylinder in a manner to form a closed air chamber, input and output coupling means projected l,into the space surrounded by said outer cylinder, a drying agent exposed to said air chamber but disposed outside thereof to maintain a constant velocity of propagation within said air chamber.

4. A coaxial conductor wavemeter, comprising a pair of cylinders of different diameters concentrically disposed one within the other and shorted at one end by a metallic disc, a second metallic disc closing the opposite end of the outer cylinder in a manner to form a closed air chamber, input and output coupling means projected into the space surrounded by said outer cylinder, a retaining means attached to and disposed outside said outer cylinder near said second metallic disc, and a drying agent disposed Within and substantially filling said retaining means to maintain a constant velocity of propagation Within said air chamber.

5. A coaxial conductor wavemeter, comprising a pair of cylinders of different diameters concentrically disposed one within the other and shorted at one end by a metallic disc, a second metallic disc closing the opposite end of the outer cylinder in a manner to form a closed air chamber, means for adjusting the lengt-h of the inner cylinder and thereby the resonant frequency of said Wavemeter, means for maintaining the length of said inner cylinder constant at any one setting over a wide range of temperature variation, input and output coupling means projected into the spacesurrounded by said outer cylinder, and hygroscopic means exposed to said air chamber but disposed outside thereof to maintain a constant velocity of propagation Within said air chamber.

6. A coaxial conductor Wavemeter, comprising a pair of cylinders of different diameters concentrically disposed one Within the other and shorted at one end by a metallic disc, a second metallic disc closing the opposite end of the outer cylinder in a manner to form a closed air chamber, input and output coupling means projected into the space surrounded by said outer cylinder, means for adjusting the length of the inner cyl- Inder and thereby the resonant frequency of said wavemeter, means for maintaining the length of said inner cylinder constant at any one setting over a Wide range of temperature variation, a drying agent exposed to said air chamber but disposed outside thereof to maintain a constant velocity of propagation Within said air chamber.

7. A coaxial conductor Wavemeter, comprising a pair of cylinders of different diameters concentrically disposed one within the other and shorted at one end by a metallic disc, a second metallic disc closing the opposite end of the outer cylinder in a manner to form a closed air chamber, input and output coupling means projected into the space surrounded by said outer cylinder, mea-ns for adjusting the length of the inner cylinder.v and thereby the resonant frequency of said wavemeter, means for maintaining the length ofsaid 20 stant velocity of propagation within said air chamber.

JOHN P. HAGEN. FRANK C. ISELY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,866,611 Alel July 12, 1932 2,103,515 Conklin Dec. 28, 1937 2,115,787 Runge May 3, 1938 2,175,025 Hooven Oct. 3, 1939 2,210,050 Usselman Aug. 6, 1940 2,215,582 Goldstine Sept. 24, 1940 2,218,923 Newhouse Oct. 22, 1940 2,235,521 Higgins Mar. 18, 1941 2,267,520 Dow Dec. 23, 1941 2,349,440 Lavoie May 23, 1944 2,365,207 Moles Dec. 19, 1944 FOREIGN PATENTS Number Country Date 337,551 Great Britain Nov. 6, 1930 501,593 Great Britain Feb. 27, 1939 

